A. Field of the Invention
The present invention pertains to a method as well as a device for preparing and opening a roll consisting of a strip of supple material spirally wound in superimposed layers and having a top layer the free end of which is attached to the layer directly beneath it, said roll being mounted on a support shaft and having two parallel sides. The method and the device according to the invention are particularly useful for relatively narrow rolls, namely, those delivering a strip having a maximum width on the order of several centimeters.
B. Description of the Related Art
Various patents, in particular EP-B No. 318,427, EP-B No. 331,634, and EP-B No. 475,886, describe different methods and devices which serve to open a roll consisting particularly of a strip of paper or other material to be fed into a manufacturing machine. These patents generally provide for a cutting blade that is perpendicular to the unwinding direction of the strip and is applied to the top layer of the roll in order to cut it. Since the cutting blade is pressed onto the top layer with a certain force and/or is inserted a certain distance into the roll, several layers of the roll generally are cut simultaneously, with no way of verifying how many layers have been cut.
With these systems, it often happens that the next layer directly below the last cut layer is damaged by the blade, thus making a weak point that could cause the strip to break at that point. A break of this type requires a shutdown of the machine, resulting in a loss of productivity. In certain cases, the top layer of the roll is covered with a protection band made of a material that can be different from that of the roll. In the following description, the top layer of the roll refers either to this protection band, if present, or to the first layer or layers of the roll.
The portion of the second layer onto which the free end of the top layer is glued generally must be removed, for which there must be available auxiliary means of removing it, such that would require that only one layer be cut in some place on said layer not in the immediate proximity of the gluing point.
The application DE-A No. 3,215,355 discloses a related device. The device described therein comprises a support bar on which are mounted a cutting blade and a layer separating blade, both the separating and cutting actions being controlled simultaneously by the movement of the support bar. This device has a number of disadvantages: the design is such that it is impossible to adjust the distance between the support bar and the separating blade, and it is fairly difficult to minimize the height travel setting for the separating blade, as a result of which an excessive number of layers must be cut.
Furthermore, if the force of the separating blade spring decreases after long use, there might not be sufficient compressive force between the support bar and the separating blade, and thus it is impossible that one or several layers between the support bar and the separating blade might not be severed properly.
Since the support bar rests directly on the top layers, the latter are compressed, which makes it more difficult to insert the separating blade. Because the advancing movements of the support bar against the upper layer and those of the separating blade are simultaneous with the cutting movement, the layers to be cut are shifted, causing damage to the layer directly beneath the separating blade and preventing a clean cut of the layers.
This device is not capable of making multiple cutting passes, and the fact that the cutting blade is attached to the support bar makes it difficult to replace a worn blade. Furthermore, this device does not have any means of relaxing the tension of the top layers of the roll if said layers are tightly rolled, in which case it is impossible to use the device.
The documents DE-A No. 3,918,552 and U.S. Pat. No. 4,821,971 describe devices for opening wide rolls. The problems encountered in this case are essentially different from those which the invention proposes to solve. In particular, these devices cannot insert the layer separating blade across the entire width of the roll.